1. Field of the Invention
The present invention relates to a power transfer device adapted for use in combination with a power transmission for a four wheel drive vehicle to transfer output drive torque of the power transmission to a pair of front road wheels and a pair of rear road wheels, and more particularly to a power transfer device capable of selectively providing either a two wheel drive or a four wheel drive.
2. Description of the Prior Art
There has been proposed a power transfer device of this kind which comprises a housing secured to one end of a transmission casing, an input shaft rotatably mounted within the housing and drivingly connected to an output shaft of the power transmission for the vehicle, a first output shaft arranged in parallel or coaxially with the input shaft for drive connection of the input shaft with front wheel or rear wheel drive axles, a second output shaft arranged coaxially or in parallel with the first output shaft for drive connection with rear wheel or front wheel drive axles, and a shift mechanism for selective connection or disconnection of the first output shaft to or from the second output shaft thereby to provide a four wheel drive or a two wheel drive.
In a Japanese Patent Publication No. 57-54333, for example, there has been proposed a shift mechanism in a power transfer device of this kind which shift mechanism includes a sleeve member axially slidably mounted on one of the first and second output shafts for connection or disconnection of the one output shaft to or from the other output shaft, a shift rod arranged in parallel with both the output shafts and axially movably supported on the peripheral wall of the housing, a shift fork mounted on the shift rod and coupled with the sleeve member for shifting the sleeve member in response to axial movement of the shift rod, an operation rod in the form of a cross-rod arranged perpendicularly to the shift rod and rotatably supported on the peripheral wall of the housing to be rotated by means of a manual operation lever, and a shift lever fixedly mounted on the operation rod for rotation therewith and being integrally provided with a swing arm which is engaged with the shift fork to effect axial movement of the shift rod in response to rotation of the operation rod.
In such a conventional shift mechanism as described above, there is provided a detent mechanism which cooperates with an interlock mechanism for selectively restricting the axial movement of the shift rod. The detent mechanism includes a spring loaded check ball selectively engageable with a pair of axially spaced recesses formed on the shift rod, and the interlock mechanism includes an interlock pin engageable with a recess formed on the shift rod. In the detent and interlock mechanisms, it is necessary to restrict rotation of the shift rod thereby to ensure selective engagement of the check ball and interlock pin with the respective recesses of the shift rod. For this reason, an additional arm is fixed to an intermediate portion of the shift rod and engaged with a stationary member in the transfer device to restrict the rotation of the shift rod. This inevitably causes the shift rod to be complicated in structure. Furthermore, axial movement of the operation rod outwardly with respect to the housing should be avoided to retain it in position. For this reason, the peripheral wall of the housing is formed to extend between boss portions respectively provided on the manual operation lever and on the shift lever so as to retain the operation rod in position. As a result of such arrangement as described above, both the side faces of the housing and each contact face of the boss portions should be machined with a required precision.